Efficient use of water and nutrients in crop production are critical for sustainable water and crop production systems. Understanding the role of humans in ensuring water and nutrient use efficiency is therefore an important ingredient of sustainable development. Crop production functions are often defined either as functions of water and nutrient deficiency or are based on economic production theory that conceptualizes production as a result of economic activities that take in inputs such as water, capital and labor and produce crop biomass as output. This paper fills a gap by consistently treating water and nutrient use and human agency in crop production, thus providing a better understanding of the role humans play in crop production. Uptake of water and nutrients are two dominant biophysical processes of crop growth while human agency, including irrigation machine power, land-preparing machine power and human labor force, determine limits of water and nutrient resources that are accessible to crops. Two crops, i.e., winter wheat and rice, which account for the majority of food crop production are considered in a rapidly developing region of the world, Jiangsu Province, China, that is witnessing the phenomenon of rural to urban migration. Its production is modeled in two steps. First water and nutrient efficiencies, defined as the ratios of observed uptake to quantities applied, are modeled as functions of labor and machine power (representing human agency). In the second step, crop yields are modeled as functions of water and nutrient efficiencies multiplied by amounts of water and fertilizers applied. As a result, crop production is predicted by first simulating water and nutrient uptake efficiencies and then determining yield as a function of water and nutrients that are actually taken up by crops. Results show that modeled relationship between water use efficiency and human agency explains 68% of observed variance for wheat and 49% for rice. The modeled relationship between nutrient use efficiency and human agency explains 49% of the variance for wheat and 56% for rice. The modeled relationships between yields and actual uptakes in the second step explain even higher percentages of observed the variance: 73% for wheat and 84% for rice. Leave-one-out cross validation of yield predictions shows that relative errors are on average within 5% of the observed yields, reinforcing the robustness of the estimated relationship and of conceptualizing crop production as a composite function of bio-physical mechanism and human agency. Interpretations based on the model reveal that after 2005, mechanization gradually led to less labor being used relative to machinery to achieve same levels of water use efficiency. Labor and irrigation equipment, on the other hand, were found to be complimentary inputs to water use efficiency. While the results suggest interventions targeting machinery are most instrumental in increasing wheat productivity, they may exasperate rural – urban migration. Policy strategies for alleviating rural-urban migration while ensuring regional food security can nonetheless be devised where appropriate data are available.

Water resources are one of the important factors that influence regional crop production and the food security of humans. Most traditional models of crop water demand analysis are built on the basis of a certain crop or macroscopic analysis, which neglect regional crop allocation and the difference of water demand in different crop growing periods. In this paper, a new assessing model, the satisfied degree of crop water requirement, is developed to assess the impacts of water resources on production of six main food crops in China. The six main food crops are spring wheat, winter wheat, corn, early season rice, middle-season rice and late rice. The results show that: (1) there are serious risks of water shortage in China, even in south China with its abundant precipitation; (2) the satisfied degree of crop water demand represents great temporal–spatial changes. On spatial distribution the risks are high in major bases of food production due to influences of cropping system and crop-combinations. Northwest China is a special interesting case. In seasonal fluctuation water shortage is severe in March and September. These risks seriously restrict food production in China. The results also show that the strategic measures of water resources management must be chosen carefully to deal with food security and regional sustainable development in China.

Located in the basalt desert of northeastern Jordan, Early Bronze Age (EBA) Jawa is regarded as one of the major settlements in the Middle East during the 4th millennium BCE. In addition to a sophisticated water storage system, the existence of three complex agricultural terrace systems based on runoff and floodwater irrigation in the close vicinity was recently revealed.This paper investigates the impact of these water management strategies on harvest yields and the scale of the ‘on-site’ crop production at Jawa by applying a crop simulation model (CropSyst). Simulations for the cultivation of winter barley, winter wheat and lentils were performed for the period from 1983 to 2014. To simulate the different runoff irrigation schemes, a curve-number-based rainfall-runoff model was applied. To estimate the number of people that could have been supplied by the local food production, simple calculations based on metabolic calorie requirements and agricultural and pastoral production rates were conducted.This study shows that the runoff farming systems of EBA Jawa are relatively effective under current rainfall conditions. Even during dryer seasons, the simulated crop yields are much higher under runoff irrigation/floodwater irrigation than under non-irrigated conditions. On average the crop yields increase by 1.5 to 6 times, depending on crop type and runoff irrigation level. Moreover, a marked decrease in crop failures could be observed. The total crop and animal production could have satisfied the nutritional requirements of about 500 to 1000 persons per year. Considering the estimated maximum population for EBA Jawa, ranging from 3400 to 5000 people (Helms, 1981), local production did not meet the basic needs of all inhabitants. This indicates that trade might have been an important branch of Jawa's economy in order to supplement food resources. Moreover, former population estimates for ancient Jawa might be overstated.

North China Plain suffers from the world’s most severe water scarcity and groundwater depletion due to intensive irrigation for agricultural production. It is imperative to reduce irrigation water consumption while safeguarding crop production and food security. This study conducted a quantitative analysis with deficit irrigation strategies for winter wheat using a water-driven AquaCrop model. After model calibration and validation with field experimental data, we analyzed the irrigation water demand, crop yield, and water productivity (WP) of winter wheat under various deficit irrigation scenarios. A set of optimal irrigation schedules were proposed for different climate years, which significantly mitigated irrigation water usage while sustaining high yields and WPs. The results indicated that despite the irrigation water demand of winter wheat under the future climate scenario was slightly higher than that in the historical period, their crop water sensitive periods (reviving, jointing, and flowering) remained the same. Therefore, we recommended adopting the same deficit irrigation schedules for the historical and future periods. In wet years, adopting a 50% deficit irrigation strategy only reduced crop yields by less than 5% compared with full irrigation, but it saved 1000–1100 m3 of water per hectare and contributed a WP higher than 1.88 kg/m3. While in normal and dry years, an optimal 25% deficit irrigation could sustain over 96% of the maximum yield, meanwhile it could save 650–800 m3/ha of water and achieve almost the same WP as full irrigation. These climate-smart irrigation strategies adapting to diverse climatic conditions largely mitigate agricultural water consumption while maximizing crop productivity and water use efficiency, which are essential for achieving precision irrigation and sustainable water management under a changing climate.

Climate change will not only affect crop biomass production but also crop quality. While increasing atmospheric CO2 concentrations are known to enhance photosynthesis and biomass production, effects on the chemical composition of plants are less well known. This is particularly true for major crop plants with respect to harvestable yield quality. Moreover, it remains open, how these effects on quality may be realized under field conditions and how management (e.g. plant N nutrition) or environmental factors (e.g. water availability) will alter impacts of elevated CO2. Here we report on a series of free air CO2 enrichment (FACE) experiments with wheat and barley and with maize in which effects of elevated CO2 combined with different levels of N supply (wheat and barley) and with drought stress (maize) on grain and biomass quality characteristics were investigated. Winter wheat and winter barley (1st experiment) and maize (2nd experiment) were grown in the field each for two growing seasons under ambient and elevated CO2 concentration (FACE, 550μmol mol-1). Wheat and barley were grown under adequate N supply and under 50% of adequate N as sub-treatments. In the maize experiment rain shelters were used to create two different levels of plant water supply (well-watered and drought stress – about 50% of well-watered) as sub-treatments. Treatment effects on elemental composition and a variety of quality characteristics of the plant material at final harvest were investigated. This included a detailed analysis of wheat grain protein components and of different fiber fractions of maize. Compiled results of the relative effects of elevated CO2, N and drought stress treatments on different quality parameters of the crops are presented.

The North China Plain (NCP) is one of the major grain production areas in China where the groundwater level has declined rapidly in recent years because of irrigation. To alleviate the pressure on water resources, in 2016, the government developed and implemented a reasonable subsidy policy, known as the Winter Fallow Policy (WFP), to fallow cultivated land in a selected pilot area in the funnel region (Heilonggang region, HR). In the present study, a large-scale household survey was conducted across the NCP groundwater overexploitation region (OR) to evaluate the possible impact of the WFP on groundwater and food security. Our survey results indicated that the education level of decision makers, the dependency ratio of farmers, laborers per cultivated area, and the magnitude of the importance of water-saving in agriculture of decision makers have significant impacts on farmers' willingness to fallow. The average ecological compensation (EC) was 8781 CNY/ha (1358 USD/ha) and varied from 6932 to 10816 CNY/ha (1072–1673 USD/ha) in different counties. Winter wheat fallow in semiarid, dry subhumid and humid areas can save approximately 4642, 3325 and 1906 m³/ha, respectively, of groundwater in the OR. In the HR, a fallow area of 0.31×10⁶ ha is recommended for maintaining the current groundwater table, and an area of 0.42×10⁶ ha is recommended for restoring or recovering groundwater resources; these areas are greater than the existing fallow area and will reduce wheat yields, accounting for 1.55% and 2.08%, respectively, of national wheat production. Thus, EC standards should be determined based on local commodity price standards and modified based on annual changes in local conditions. Furthermore, the winter fallow acreage should be expanded in the HR to maintain the groundwater table.

The increasing dependency on groundwater, especially in irrigated regions, has highlighted the notable place of groundwater resources within the water-food-energy nexus (WFEN). This role is particularly relevant in the Haihe River basin of China, a globally representative area that is experiencing rapid aquifer depletion. The winter wheat (Triticum aestivum L.) fallow strategy may have the potential to limit withdrawal in this region. Based on information from multiple sources, this paper proposed six kinds of fallow schemes—under the same triple-cropping system consisting of winter wheat and summer maize (Zea mays L.) followed by fallow and summer maize in two years (WW–SM/F–SM) but with different irrigation schemes—as scenarios to conduct detailed simulation by a modified Soil and Water Assessment Tool (SWAT) model. Then, the water balance components of the shallow aquifer and soil profile (2 m) under different scenarios were analyzed to quantify the variations in hydrological processes caused by changes in cropping system and pumping intensity. Furthermore, through 17 indices that could quantitatively describe the changes related to the WFEN, the effects of seasonal fallow schemes on shallow groundwater drawdown mitigation, grain yield reduction, and energy consumption savings were evaluated. Based on these evaluation outcomes, linear programming was used to optimize the fallow schemes at the subbasin scale. As a result, to satisfy the constraint of stopping groundwater drawdown as well as improving water and energy productivities, the minimum reduction in the annual average winter wheat yield would be 55% compared with the basic scenario, while the summer maize yield would remain basically stable. Under the optimized fallow scheme pattern, 66% of the well-irrigated cropland should adopt the WW–SM/F–SM system with two irrigation applications for winter wheat and a rain-fed scheme for summer maize; additionally, 24% of the well-irrigated cropland should adopt the WW–SM/F–SM system with one irrigation application for winter wheat and a rain-fed scheme for summer maize, and the recommended fallow schemes for the other 10% of well-irrigated cropland varied spatially. Compared to the basic scenario, the optimized fallow scheme pattern could decrease shallow groundwater exploitation by 36.5 × 10⁸ m³ a⁻¹ (i.e., to realize shallow groundwater equilibrium), reduce the diesel consumption of agricultural machines and electricity consumption of pumping wells by 32% and 90%, respectively, and save energy costs by approximately 873 yuan ha⁻¹. These results could provide a quantitative reference for policy-making in this watershed and serve as a typical case for similar areas that wish to implement fallow strategies to achieve groundwater sustainability.